Spring brake actuators of this type are well known in the art. Normally they are attached to the cylinder and form an elongation of the unit. In such a case the spring brake actuator piston rod acts on the brake unit piston for applying the force of the spring at parking or emergency braking, when the spring is not compressed under the action of a brake fluid pressure on the opposite side of the actuator piston.
In some instances it has been found more advantageous to arrange the spring brake actuator around the rod-shaped member of the brake unit, whereby the disadvantage with the added length is obviated, but still these designs are bulky and suffer from drawbacks.
It is desirable to see the brake unit as the basis for a modular system, whereby different functions of the system may be obtained.
The object of this invention is basically to combine the advantages of a spring brake actuator arranged around the rod-shaped member of the brake unit and the advantages of the truly modular system.